1. Field of the Invention
The present invention relates to the field of data communications networks. More particularly, this invention relates to a method and apparatus for resolving Domain Name Service requests in a data communications network.
2. The Background
The Service Selection Gateway (SSG) is a product which allows data communications network users to select and login to services available on the data communications network. These services can include computer intranets, pay per use sites, the Internet, community of interest services and the like. The SSG permits a user to simultaneously log in to a plurality of such services, even if they have overlapping IP address space.
Each service to which a user may be connected has an associated IP (Internet Protocol) address space. That is, a certain range of addresses may address that space. The range may be contiguous, discontiguous, or a combination of both. For example, Corp A may have an intranet service having all IP addresses which start with “10.1”—this may be denoted “10.1.x.x” where x can be any value. It may also be denoted “10.1.0.0; 255.255.0.0” where “10.1.0.0” represents the IP address and “255.255.0.0” represents the subnet mask. Those of skill in the art will recognize that a 255 in the subnet mask field represents a binary 1111 1111 and amounts to a requirement that the corresponding field of the IP address must match bit for bit in order to achieve a match. On the other hand, a 0 in the subnet mask field represents a binary 0000 0000 and amounts to no requirement for any match. For example, a service having an address space of “0.0.0.0; 0.0.0.0” represents the Internet, i.e., all IP addresses are within this space. Note that since the subnet mask is 0.0.0.0 the IP address could be set to any value and it would yield the same result.
In data communications networks a domain name service (DNS) is used to resolve textual domain name strings, such as “CORPA.COM”, into numerical IP addresses which can be used to route packets to and from such domains. A DNS system typically includes a hierarchy of DNS servers distributed throughout the network. A DNS request is generated, for example, by a user running an Internet browser application program on a computer. The DNS request is then forwarded to a DNS server associated with the user's account as often determined by settings set in software (typically the user's operating system) by the user. If the DNS request can be handled at that level, the numerical IP address is passed back to the user's application. If not, the request is passed to a superior DNS service, and so on.
Where the user is logged into more than one service, more than one DNS service may be available to service the user's DNS requests. This leads to a conflict. In some cases one of the DNS services will be “better” to use than another in that it may be more likely to quickly resolve the DNS request, however, the settings in the user's operating system may undesirably direct the DNS request packet to the “wrong” DNS service. Accordingly, it would be desirable to provide a method and apparatus for resolving where to forward DNS requests from a user with more than one concurrent service connection on a data communications network.